1. Field of the Invention
The present invention relates to a pulley unit to be mounted in an auxiliary device, which is a device driven by a belt combined with a crank shaft of an engine of a vehicle, for example. Examples of such an auxiliary device are a compressor for an air conditioner, a water pump, an alternator, and a cooling fan of a vehicle, for example.
2. Description of the Related Art
An example of such a pulley unit in the prior art is shown in FIGS. 8 and 9. In those figures, reference numerals 81, 82, 83 and 84 denote, respectively, a pulley, a shaft, a one-way clutch and a rolling bearing. The one-way clutch 83 has an inner ring 85, an outer ring 86, a plurality of rollers 87, cage 88 and a coil spring 89.
When the cage 88 in such a one-way clutch 83 jolts in the angular and/or axial direction with respect to the inner ring 85, the functions of the locking in and the releasing free of the one-way clutch 83 tend to be unstable. Therefore, two radially inward directed projections 90, 90 having different angular positions are provided on one of the shaft ends of the cage 88, and two slits 91, 91 having different angular positions are provided on one of the ends of the inner ring 85; the projections 90, 90 and the slits 91, 91 are engaged with each other in the axial direction thereof so that the cage 88 is positioned exactly at a predetermined position in the angular direction and in the axial direction with respect to the inner ring 85 in order to prevent such instability.
There is room for improvement in the positioning of the cage 88 in the one-way clutch 83 in the prior art.
In the prior art, the inner ring 85 is forced fit around the shaft 82 by force so that the rotation around the shaft is prevented. However the forced fitting causes a stress acting to the inner ring 85 in the angular direction. The stress tends to concentrate to the inner corner of the slits 91, 91 of the inner ring 85. Thus there is danger of cracking of the inner ring 85 starting from the stress concentrated point.
Other problems are the low efficiency of the working to form the slits 91, 91, and the necessity of the treatment afterward for removing burr. Therefore the fabrication cost is expensive.
A primary object of the present invention is to provide a pulley unit, comprising the structure of the axial positioning of the cage of the one-way clutch, which has no structurally fragile portion while achieving a simplified fabrication procedure.
Other objects, features, and advantages of the present invention will be apparent from the following description.
The pulley unit according to the present invention includes: an inner shaft, an external ring disposed concentrically around the inner shaft, and a one-way clutch disposed in an annular space between the inner shaft and the external ring having a plurality of rollers, and two rolling bearings disposed in the annular space; each of the rolling bearings is fixed in the axial direction respectively at each side of the one-way clutch; the one-way clutch comprises a cage for constraining the rolling region of the plurality of the rollers; the inner diameter of the cage is designed to be smaller than that of the orbital portion of the inner ring of one of the rolling bearing.
Due to the structure according to the present invention, the movement of the cage in the pulley unit is constrained in an axial direction, without using the recessing and projecting portions for constraining such a movement, which are disposed in the cage and the inner ring of the pulley unit in the prior art. Therefore, the structure of the pulley unit can be simplified and structurally fragile portions can be eliminated. Moreover, the fabrication processes to form such recessing and projecting portions can be omitted, thus the fabrication cost can be reduced.
The inner diameter of the cage according to the present invention is, preferably, smaller than the outer diameter of the inner ring orbital portion of the other rolling bearing. Due to such a structure, the movement of the cage is constrained in both of the axial directions.